Electrical Apparatus, July 2014

Electrical Apparatus, July 2014

This is a summary of the Electrical Apparatus July 2014 featured technical article,  by Richard L. Nailen, P.E.  

Enough pollution-free solar radiation reaches us to supply the world’s energy needs. The ideal utilization of this energy is its photovoltaic (PV) conversion to electricity. The technology has been developing rapidly.

However, the path has not been smooth. Despite optimistic predictions by industry suppliers and government agencies, PV produces only about 1% of U.S. electrical energy demand. In Germany, the world’s largest PV energy user, the figure is only 5%.

A PV system involves three components. Drawing the most attention, despite being only a small part of overall system cost, is the solar panel in which the energy conversion occurs. China, where panel manufacturers enjoy government support, is now the world’s leading supplier. The price of panels has dropped dramatically, forcing many panel manufacturers out of business in Europe and the U.S. The emphasis now is on increasing conversion efficiency, which has been less than 25%.

The second PV component is the inverter coupling d-c panel output to a-c loads or the utility grid. This technology is also evolving. Any interface between solar collector and connected electrical system must deal with voltage sags, power flow, and circuit protection.

The third system component is the structure itself. In open areas without overshadowing surroundings, large-scale solar arrays are being built with ratings of 500 megawatts or more. Power may be contracted to the public utility, which may own the facility. While some utilities have embraced PV, others view it as a threat.

In urban areas, roofs of commercial and industrial buildings are becoming PV sites. Thousands of panels may be installed with overall ratings of 5 megawatts or more. Home rooftops are similarly utilized for arrays in the 1 to 5 kilowatt range. Whereas provisions are often made for maintenance and repair of the larger commercial or industrial installations, the residential homeowner may have little recourse as systems age. Some authorities therefore see the real future of photovoltaics in “industrial-scale” installations.

Now recognized, following several disastrous building fires, are safety hazards of rooftop installations. First, since solar panels remain energized whenever illuminated, firefighters are exposed to electric shock, and cannot safely work on roofs to cut openings needed for venting smoke and gases. Second, without that venting, interior firefighting may become impossible.

Also, water streams directed at a burning roof are deflected by the solar panels, the extra weight of which can hasten roof collapse. Agencies in the U.S. have begun revising safety codes and undertaking research projects to deal with these issues.

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